Inertia operated switching device



April 8, 1958 THOMSON 2,830,147

INERTIA OPERATED SWITCHING DEVICE Filed Dec 29, 1954 United States atent INERTIA OPERATED SWITCHING DEVICE Edward Thomson, Mount Vernon, Ill.

Application December 29, 1954, Serial No. 478,267

12 Claims. (Cl. 200--61.46)

My invention relates to inertia operated switching devices in general and particularly to those switching devices for interrupting an electrical circuit to a drive motor when a load shock is sensed. More particularly this invention relates to a switching device responsive to sudden changes in load applied to a prime mover, such changes being sensed by means responsive to an inertia force which causes relative motion between two or more members.

Prior inertia operated switching devices have been made utilizing the difierence in inertia between rotating members to produce relative motion between members for operating switching contacts. However, in none of these has provision been made for releasing a second force to operate the switch which second force is released as a result of the inertia force and acts along the axis of the moving members and normal to the inertia force. Prior inertia operated switching devices have used over-center springs and magnets for supplying the force in opposition to the inertia force and the switching contacts have been operated directly by the inertia force through a variety of cam arrangements. One disadvantage apparent in such a system lies in the fact that once the contacts have been placed in the operative condition as a result of the inertia force, a jar or reverse inertia force may cause the repositioning of the cam and return the switch contacts to the inoperative state where the drive motor will undesirably restart. Such a danger creates a safety hazard.

An advantage the present inertia operated switching device has over a prior ineitia switching devices is in the construction of the device for directly operating the switch itself. Another advantage is found in the construction whereby the switch contacts need not be mounted on a movable member. This eliminates all need for brushes, commutators and slip rings which are required where the switch contacts move. This also facilitates access to the switch and its contacts for cleaning and adjusting.

Still another advantage achieved by the present invention over prior inertia operated switching devices is found in the reset mechanism. The reset mechanisms formerly used have included a second switch apart from the inertia switch for shorting the contacts of the inertia switch when restarting the drive motor. If this second switch for resetting should become faulty or if the operator should fail to reposition it after using it to restart the drive motor, or if the operator should accidentally bump into the reset switch after the shock load has stopped the drive motor, the drive motor might restart; creating a safety hazard. The mechanical-magnetic reset means used in this invention can not reset itself undesirably because the inertia switch is held by spring tension in its operative condition after the inertia force has released the inertia switch operating mechanism. The reset means can not short out the inertia switch contacts either because the reset means are mechanical and not electrical. Furthenit is not likely the reset switch will be inad- "ice vertently reset because a spring pressure is holding it in its operative condition.

It is a major object of the present invention to provide an inertia operated switching device that responds to load shocks over a wide range of speeds and for predetermined amounts of inertia force.

It is an object of this invention to provide an inertia operated switching device that requires no slip rings, commutators, brushes or reset switches.

It is an object of the present invention to provide an inertia operated switching device that will sense load shocks in a rotating system for either direction of rotation and which can be installed for this reason in a greater variety of locations with respect to the prime mover.

it is an object of the present invention to provide an inertia operated switching device which remains in the released condition once a shock load is sensed and which can not be reset undesirably.

it is an object of the present invention to provide an inertia operated switching device which uses the relative motion between movable members brought about by the force of inertia when a shock load is sensed to release a force for operating the switch, which force pperates along the axis of rotation normal to the inertia orce.

A further object of the invention is to provide an inertia operated switching device that can be adjusted to a predetermined shock load condition. More particularly it is an object of the present invention to provide an inertia operated device wherein magnetic elements are employed to give a force tending to prevent relative movement between members which magnetic force may be varied depending upon the sensitivity desired.

Another object of the invention is to reduce the number of parts necessary in an inertia operated switching device.

This invention consists in the provision of an inertia operated switching device operably connected to a prime mover wherein a switching contact is made or broken in response to relative motion between two members caused by a rate of change in external conditions greater than a predetermined rate usually resulting when a shock load is sensed by the prime mover. The relative motion between members produced by the inertia force causes the switching to take place through an intermediate device operating normal to the inertia force.

The invention further consists in those parts, elements and components which will be described herein, or which are the equivalent thereto. The description will bedirected to the several views of the drawings, wherein:

Fig. 1 is a side elevational view of the device incorporating the invention;

Fig. 2 is an end elevational view or the device shown in Fig. 1 looking at it from the right;

Fig. 3 is a sectional elevational view along the line 3-3 in Fig. 4;

Fig. 4 is a transverse section-a1 view along line 4-4 in Fig. 3;

Fig. 5 is a view similar to Fig. 3, but taken along line 5-5 in Fig. 6;

Fig. 6 is a transverse sectional view along line 6-6 in Fig. 5;

Fig. 7 is a sectional detail view along line 77 in Fig. 4; and

Fig. 8 is a sectional detail view along line 88 in Fig. 6.

The invention is disclosed in a preferred embodiment in the several views of the drawings in which the numeral 10 designates the housing for the inertia operated switching device. Extending centrally from one end of the housing 10 shown in Fig. 1 is a tubular shaft 12 which.

carries spaced bearings 14a and 14b at the ends of the tubular shaft 12.

Rotatably carried within the bearings 14a and 14b is a shaft 16 which forms a part of a driving member 18 to be later described. Between the bearings 14a and 14b in the tubular shaft 12 is a hollow space 20 suitable for holding a lubricant. At one end of the shaft 16, shown as the left end in Fig. l, is a pulley 22 fixedly connected thereto and prevented from rotating relative to the shaft 16 by suitable means such as a key, a set screw or a combination thereof (not shown).

The opposite end of the shaft 16 extends into the housing 10 and has an axial counterbore 24 therein. The counterbore 24 is shown directed along the axis of the shaft 16 and the end of the shaft 16 is shown tapered or rounded.

Two fin-like armatures 26a and 26b are shown in Fig. 4 fixedly connected to the shaft 16 and extending away from the center thereof in diametrically opposite directions. and 26b have large lateral surfaces and are narrow in cross section, as shown in Figs. 3 and 4.

An elongated cross bore or slot 23 passes through the shaft in the region of the fin-like armatures 26a and 26b. The slot 28 intersects the counterbore 24 in the end of the shaft 16 and in the preferred construction is at right angles with the fin-like armatures 26a and 26b. The slot 28 is adapted to slidably receive therethrough a cross-arm portion 30 of a T shape plunger 32. The T shaped plunger 32 has a central elongated plunger portion 34 at right angles with the cross-arm portion 30. The central portion 34 is slidably positioned in the counterbore 24 between the cross-arm 30 positioned in the slot 28 and the end of the shaft 16 and extends from the end of the shaft 16 a distance depending on the position of the T member 32 which will be later described.

Positioned on the cross-arm portion 30 opposite the elongated central portion 34 is a positioning stud 36 suitable for maintaining a compression spring 38, located in the counterbore 24 between the seat of the counterbore 24 and the cross-arm portion 30 of the T member 32 in engagement with the T member 32. The compression spring 38 urges the T member 32 in a rightward position (as viewed in Figs. 1, 3 and 5) at all times. The shaft 16, armatures 26a and 26b, and T member 32 make up the driving member 18.

The armatures 26a and 26b and the cross-arm portion 39 of the T member 32 are parts of the driving assembly positioned in a relatively movable, flywheel type inertia sub-assembly 42. The inertia sub-assembly 42 is sensitive to a shock load and causes operation of a switching device hereinafter described to shut ofi? the power to the prime mover before the overload caused by the shock reaches the prime mover. Therefore, this device functions as a safety means to save the machine or tool from the eflects of destructive forces which would develop if the overload were allowed to build up. An end plate 44, loosely mounted upon the shaft 16 is located between the armatures 26a and 26b and the left end of the housing 10 as shown in Figs. 1, 3 and 5. Another end plate 46 also loosely mounted upon the shaft 16 is located on the opposite side of the armatures 26a and 261) from the end plate 44. An inertia member 48 is positioned between the end plates 44 and 46 near their outer periphery. The inertia member 48 has a large mass and is desirably made of a non-magnetic material, as are the plates 44 and 46. Carried by the inertia sub-assembly 42 near the inner surface of the inertia member 48 are two magnetic members 50 as shown in Figs. 4 and 6 having a suitable arcuate form so that they will fit closely the inner surface"- or contour 52 of the inertia member '48.

The ends of each of the magnetic members 50 are shown formed into cars 54. The ears 54 are turned toward the center of the device to enable fasteningmeans 56, shown as screws, passing between the end plates 44 In the preferred construction the armatures 26a 1.,

and 46 to hold the magnetic members in a fixed position thereb'etween.

The inertia sub-assembly 42 is loosely or rotatably carried on the shaft 16 of the driving member 18, so that the armatures 26a and 26b are movable relative to the inertia sub-assembly 42 in the space between the ends of the magnetic members 50. The cross-arm portion 30 of the T member 32 which passes through the slot 28 in the shaft 16 simultaneously turns with the shaft 16 at right angles with the armatures 26a and 26b.

Positioning studs are located on one of the end plates, as on the end plate 46 of the inertia sub-assembly 42 and extend from end plate 46 in the direction of end plate 44. In Figs. 4 and 6, four such studs 60 are shown. The studs 60 are positioned on the end plate 46 such that the cross-arm portion 30 of the T member 32 will engage on the end surface thereof when in a normal condition of the cross-arm portion 30. In the energized condition just after a shock load has been sensed (see Fig. 8) the cross-arm portion 30 will be caused to slide off the end of the studs and find a position in the space between opposite pairs of the positioning studs 60 as will be later described. Which two opposite studs 60 the cross-arm portion 31) will rest upon in the normal or operative condition, will depend upon the direction of rotation of the driving member 18.

The same end plate 46 that carries the studs 60 also carries adjustable means, shown in Figs. 3, 5 and 7 as a screw 62 having a tapered point 64 which cooperates with the beveled face 66 on the armature 26b, for varying the air gap and, hence, the magnetic force of attraction between the magnets 50 and the armatures 26a and 26b, as shown in Fig. 7. The armatures 26a and 26b are prevented from moving beyond the position shown in Fig. 6 by a non-magnetic stop screw means located in that one of the tapped holes 67 in plate 46 near the armature 26a to balance the screw 62. This location is for clockwise rotation of the armatures. Reverse rotation could be provided for by moving screws 65 to the opposite hole 67 (Figs. 4 and 6) and moving screw 62 to the position 62' as shown in the same views. A lock nut 68 is provided to maintain the setting of the adjustable means 62 once it is determined.

Located on an end housing cover 70 positioned opposite the tubular shaft 12 is a switch sub-assembly 72. Either a make or a break type switch is contemplated, but for the purpose of this description the break type will be considered because it is the more common type in a circuit breaker system. The break-type switch subassembly 72 consists of stationary terminals 74, locations for two being shown in Fig. 2. The stationary terminals 74 are fixedly secured to the end housing cover 70 by a suitable insulated fastening means shown in Fig. 3 and Fig. 5. Each of the fastening means consists of a hollow tubular insulator 76 held in position between two flat insulators 78 and 89 by a mounting screw 82 and a cooperating nut 84. Fig. 2 shows locations for two such screws 82, nuts 84 and tubular insulators 76. The stationary terminals 74 are held in position on the insulator 78 by screws 56 and cooperating nuts $8. Connected to one of the stationary terminals 74 is a lead 91 shown entering the housing cover 70 from an external location. Another load 92 connects the opposite stationary terminal 74 and goes to an external location through the end cover 70. Leads 99 and 92 are shown in a common cable for convenience.

Movable terminals 94 are normally urged into engagement with the stationary terminals '74 by springs 96 and 98 as shown in Fig. 3. The movable terminals 94, are carried by a floating insulated member 100 and fastened thereon by suitable means shown in Fig. 3 and Fig. 5 as mounting screws 102, lock washers 104 and fastening nuts 1&6. Connected between the movable terminals 94 by means of the mounting screws 98 and nuts 102 is a jumper lead 108 which makes the movable terminals 94 common electrically.

'In normal position the cross-arm portion 30 of the T member 32 rests on the surfaces of the studs 60 as discussed above. In this position the plunger portion 34 of the T member 32 is in its leftward position (Fig. 3) and the stationary terminals 74 are engaged with the movable terminals 94. This has the effect of making leads 90 and 92 common electrically. When activated by a shock load the plunger portion 34 is turned to a position where it can be extended, as will be shown. The action of the spring 38 carried in the counterbore 24 of the shaft 16 moves the plunger outwardly so that the floating insulator member 1119 of the switch sub-assembly 72 is moved and separates the movable terminals 94 from the stationary terminals 74.

A reset button 110 for restoring the switching device to its normal operating condition is connected to a reset shaft 112 that is slidably carried by the housing end cover 70. The reset shaft 112 carries a rounded head 114 on the end opposite the reset button 110 that is interposed between the movable terminal mounting insulator 106 on the switch sub-assembly 72 and the plunger member 34. The rounded head 114 is moved to the right by the plunger 34 when a shock load is sensed and moved to the left for restoring the switch terminals 74 and 94 and the T member 32 to their normal positions after the trouble is corrected. The reset shaft 112 carries the compression spring 96 positioned between the end cover 70 and the movable insulator 1%. The spring 98 is retained in place by the screw 116 and nut 118. Together the springs 96 and 93 bias the movable terminals 94 into engagement with the stationary terminals 74 during normal operation.

Fig. 8 shows an enlarged view of one end of the crossarm portion 3%) of the T member 32 as it is positioned after a shock load has been sensed.

Operation In normal operation the pulley 22 fastened to the shaft 16 outside of the housing 19 is turned at a speed that is proportional with the speed of the Working machine (not shown). Any rotary machine or vehicle which might undergo shock loads is a suitable subject for the present invention. A few illustrations of suitable subjects are electric drill presses, power lawn mowers, power saws, electric planers and grinders, lathes, etc. The present device should be located as close as possible to the normal or expected place on or in the subject means where a shock can originate so that it may function prior to the shock passing to the drive for the same.

With the pulley 22 connected to the subject means by a V-belt 12% in Fig. l, the driving member 18 will move to have the armatures 26a and 26b thereof engage the screw 62 so that the flywheel sub-assembly 42 will rotate. The tubular shaft 12 and housing are held in a fixed position. The belt is one convenient means, but other means, such as gears, chains, etc. may be used.

In normal condition the cross-arm portion 30 of the T member 32 is preset to rest on a pair of oppositely positioned studs 60 and the armatures 26a and .2615 are selectively engaged with the opposite end faces of the magnetic members 511 depending on the direction of rotation. If a sensitive condition is desired, the adjustment means 62 (Fig. 7) may be turned up to be interposed between the adjacent magnet 50 and the bevel 66 on the armature 26b. The drive is then through the tapered end 64 so that the air gap will be preserved. The further the armatures 26a and 26b are spaced by means 62 from the magnetic members 51 during normal operation the weaker will be the magnetic force therebetween and the more sensitive will the device he to shock loads.

Assuming that the driving member 18 is rotating clockwise to correspond to the condition shown in Fig. 4, when a shock load is sensed the member 18 will try to slow down (deceleration), but the inertia sub-assembly 42 will attempt to continue to rotate at the same rate in the clockwise direcion. Consequently the inertia sub-assembly 42 will move relative to the driven member 18. When the relative movement causes the parts to reach the position of Fig. 6, the cross-arm portion 30 aligns itself between opposite pairs of studs 60, thereby releasing the energy stored in the spring 38 carried in the counterbore 24 to move the T member 32 axially to the right as shown in Fig. 5 until the cross-arm member 30 reaches a fully seated condition between the studs 60. This movement of the T member 32 operates against the rounded head 114 on the reset shaft 112 that is engaged with the insulated member 190 on which is carried the movable contact terminal 94. This movement breaks the circuit of leads and 92 through the terminals 74 and 94. In the usual situation the terminals 74 and 94 are in the circuit to the drive motor of the subject machine and when broken will stop the drive motor.

Once the subject machine has been stopped it can not be restarted until the reset button has been depressed. Depressing the reset button 110 moves the round head 114 on the reset shaft 112 against the T member 32 and compresses the spring 38 carried in the counterbore 24 of the shaft 16 restoring the energy in this means. When the T member 32 has moved far enough to permit its cross-arm portion 31) to clear the studs 60 the switch 72 will close and this will restart the prime mover to set the device in rotation. The initial rotation of shaft 16 will rotate the assembly 18, thus causing the armatures 26a and 26b to move in the proper direction for moving the arm 30 over the studs 60 and re-establishing the device for proper operation. The prime mover and the tool must, of course, be cleared of any obstruction which caused initial cut-out. It is important to bear in mind that the connecting drive for the present device, as belt or its equivalent, must be as short as possible, or it must be designed to sense a shock load before the load can pass beyond to the prime mover.

The adjustable screw 62 is preferably made of a magnetic material and the lines of magnetic flux set up in the armature 2611 will extend into this screw. These lines of flux tend to establish a small attarctive force between the armature 26b and the screw 62 to prevent small shocks and vibrations from undesirably operating the switch.

.It is also preferred that the magnets 50 be positioned with their poles as shown in Figs. 4 and 6. Experimentally it is found that a more desirable condition exists with the north poles near each other and the south poles near each other. However, the device provided with a single magnet will be satisfactory.

What I claim is:

1. An inertia operated switching device, comprising a drive member connected to an external driven unit to be responsive to changes in the speed of the unit, an inertia member carried by the drive member and movable relative thereto, magnetic means located on the inertia member, armature means on said drive member cooperating with the magnetic means for exerting force therewith to limit relative movement between the drive member and the inertia member, a switch actuator carried by said drive member and movable between a condition in which the actuator is resiliently and magnetically retained in inactive condition during normal operation of the device and a condition when released in response to relative rotational movement between the driven member and the inertia member caused by a change in speed in the external driven unit in which the actuator is moved axially by release of the resilient retaining means into an active condition, and switch means contacted by said switch actuator and moved thereby from the normal condition in which the switch activator is resiliently and magnetically retained and an operative condition in which the switch actuator has been released and has moved axially.

2. An inertia operated switching device, comprising a drive member movable by and responsive to speed changes in an external driven unit, an inertia member carried by the drive member and movable relative thereto when a speed change occurs in the external driven unit, magnetic means carried by the drive and inertia members for restricting relative motion therebetween, a switch actuator carried by the drive member and movable radially and axially relative thereto from an inactive position into an activated position when aspeed change in the external driven unit results in predetermined relative rotational movement between the drive member and the inertia member, and switch means operable beween a normal position when the actuator is inactive and a switched position in response to said predetermined relative movement between the drive member and the inertia member.

3. An inertia operated switching device comprising a first member rotated in response to rotation of an external driven unit and responsive to changes in the speed of the external driven unit, an inertia member rotatably carried by the first member so as to rotate relative thereto, cooperating magnetic means carried by said inertia member and said first member for magnetically restricting relative motion between said members, a switch actuator carried by one of said members and normally biased to a tie-energized position during rotational operation of the external driven unit and releasable axially into an energized position in response to predetermined relative motion between the inertia member and the drive member, a switch carried by the device and adapted to move between the de-energized and the energized positions responsive to changes in the axial position of said switch actuator, and axially movable reset means on-the device for restoring the switch and the switch actuator to the de-energized position.

4. An inertia operated switching device, comprising a drive membermovable by and responsive to a change in speed of an external driven unit, an inertia member concentrically carried by the drive member and movable relative thereto, magnetic means carried by the inertia member and the drive member for restricting relative motion therebetween, a switch actuator carried by one of said members and biased axially relative thereto into a de-activated condition during normal operation of the external driven unit and releasable for axial movement into an activated condition when a change in speed of the external driven unit results in relative motion between the inertia member and the drive member, and a switch movable between an open position and a closed position in response to a change in the axial location of the switch actuator.

5. A safety device comprising a mounting support, a rotary member in saidrsupport, spring loaded plunger means carried by said rotary member and axially movable, in said rotary member, a flywheel member including magnetic means mounted on said rotary member for rotation relative thereto, cooperating magnetic armature means fixed on said rotary member to impart a rotary driving force to said flywheel member and be magnetical-ly attracted to said magnetic means, stud elements carried by said flywheel member adapted to be engaged bysaid plunger means with said magnetic means and magnetic armature means in cooperating driving relation, relative rotary movement between said rotary and flywheel members causing movement of said armature means away from said magnetic means to a predetermined position disengaging said plunger means and stud elements to release said plunger means axially in said rotary member, and a control switch on said support in position to be actuated upon release of said plunger means.

6. The safety device of claim 5, wherein said control 3 switch includes reset means engageable with said plunger means to restore the latter to a position to re-engage said stud elements.

7. The safety device of claim 5, wherein stop means are carried by said flywheel member to intercept said armature means at said predetermined position.

8. An inertia operated switching device, comprising a drive member connected to an external driven unit to be responsive to changes in the speed of the unit, an inertia member carried by the drive member and rotatively movable relative thereto, a magnet locatedin said inertia member, cooperating means on said drive member for exerting force on said inertia member and cooperating with said magnet to limit relative rotative movement therebetween, a switch actuator carried by said drive member and movable axially thereon between a condition in which the actuator is r siliently retained in inactive condition during normal operation of the device and a condition when released by relative rotative movement between the driven member and the inertia member caused by a change in speed in the external driven unit, and switch means contacted by said switch actuator and moved thereby from a normal condition in which the switch activator is resiliently retained and an operative condition in which the switch actuator has been released.

9. In an inertia operated switching device, a driven member, an inertia member carried by the driven member and capable of moving relative thereto, magnetic means including a magnetized element carried by and movable with the inertia member and a cooperating armature carried by the driven member adjacent said magnetized element, said armature being rotatively movable relative to both of said members, said magnetized element and said armature cooperating to restrict relative movement between said inertia and driven members, and a switch actuator carried in a de-activated condition by said armature during normal operation of the device including yieldable means adapted to displace said actuator in an axial direction to an activated position whenever the armature moves a predetermined distance away from the magnetized element in response to predetermined relative rotatable movement between the inertia and driven members.

10. A safety device comprising a mounting support, a rotary member in said support, spring loaded plunger means carried by said rotary member, a flywheel member including magnetic means mounted on said rotary member for rotation relative thereto, cooperating magnetic armature means fixed on said rotary member to impart a rotary driving force to said flywheel member and be magnetically attracted to said magnetic means, an adjustable element formed of a magnetic material carried by one of said members for varying the magnetic attraction between said magnetic means and said cooperating magnetrc armature means, stud elements carried by said flywheel member to be engaged by said plunger means with said magnetic means and said magnetic armature means in cooperatingvdriving relation, relative rotary movement between said rotary and flywheel members causing movement of said armature means away from said magnetic means to a predetermined position disengaging said plunger means and stud elements to release said plunger means, and a control switch on said support in position to be actuated upon release of said plunger means.

ll. A safety device comprising a mounting support, a rotary member in said support, spring loaded plunger means having a transverse arm carried by said rotary member and axially movable in said rotary member, a flywheel member including magnetic means mounted on said rotary member for rotation relative thereto, coopcrating magnetic armature means fixed on said rotary member to impart a rotary driving force to said flywheel member and be magnetically attracted to said magnetic means, stud elements having flat end faces carried by said flywheel member adapted to be engaged on said fiat end faces by the transverse arm of said plunger means when said magnetic means and said magnetic armature means are in cooperating driving relation, relative rotary movement between said rotary and flywheel members causing movement of said armature means away from said magnetic means to a predetermined position disengaging said transverse arm and stud elements to release said plunger means, and a control switch on said support in position to be actuated upon release of said plunger means.

12. A shock load release switch comprising a casing, a shaft rotatably mounted therein, an annular inertia de vice mounted on said shaft for rotation with or relative 15 to said shaft, a magnet carried by said inertia device, an armature carried in spring loaded condition on said shaft and axially movable relative thereto, said armature being positioned adjacent to said magnet for coupling the inertia device to the shaft during normal operation, said spring loaded armature moving axially relative to the shaft whenever the inertia member rotatively moves a predetermined distance relative to the shaft in response to a shock load, and a switch mounted on the shaft including an operating member engaged by said armature and movable between an energized and de-energized'po- 10 sition in response to the axial movement of the armature.

References Cited in the file of this patent UNITED STATES PATENTS 2,294,605 Newell Sept. 1, 1942 2,294,606 Newell Sept. 1, 1942 2,472,181 Werth June 7, 1949 2,727,041 Thomson May 22, 1956 

